Science Spotlight

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CDFW expanding efforts to restore severely declining monarch population
  • June 22, 2021
monarch butterfly on a milkweed leaf

A male adult monarch on a milkweed leaf
 

Scientist Hillary Sardiñas, who works as CDFW’s pollinator coordinator in the Wildlife Diversity Program, recalls a moment several years ago when she showed her young daughter a monarch caterpillar, and realized it’s a species her daughter might not grow up to enjoy.

“It really hit home in a personal way how important it is to conserve the species,” said Sardiñas.

The population of migratory western monarchs has declined more than 99 percent since the 1980s when millions overwintered in groves along the California coast. By the mid-2010s, the population had dropped to the hundreds of thousands. Just a few years ago, scientists estimated there were only 30,000 left. Now there are only about 2,000 migratory western monarchs left statewide.

“Western monarchs may be headed toward extinction in California, and we need to take drastic and immediate action to help recover the population,” said Sardiñas.

Western monarchs overwinter along the California coast from San Diego to Mendocino County, expanding during springtime along the Central Coast and Central Valley. They ultimately migrate into other states west of the Rocky Mountains to breed.

The drastic population decline has been attributed to several factors including habitat loss, climate change and exposure to pesticides. Western monarchs’ overwintering habitats continue to be destroyed or altered by human development, especially along the Central Coast. Development is also reducing nectar resources. Climate change may be causing monarchs to leave overwintering sites earlier than usual and before milkweed, their host plant, has fully bloomed. This causes what scientists call a “phenological mismatch,” meaning monarchs at times don’t have a place to lay eggs and lack the ability to create the next generation in their multi-generational life-cycle.

In addition to population decline, scientists are seeing a new and possibly dangerous phenomenon—an increase in resident monarchs that remain along the coast year-round and don’t migrate. These monarchs are encouraged to stick around by a non-native milkweed which allows them to breed all throughout the year. The phenomenon might seem like a novel adaptation, but scientists are finding that resident monarchs can have up to 10 times the occurrence of a protozoan parasite known as OE (Ophryocystis elektroscirrha). OE can be transmitted through contact with milkweed leaves, and leads to wing deformation, poor health, decreased reproductive ability or death.

To conserve the population, CDFW is taking action on several fronts:

  • In partnership with the Western Association of Fish and Wildlife Agencies, CDFW helped develop a 50-year management plan for western monarch conservation, published in 2019. Two major focus areas of the plan are management of overwintering sites on the California coast and restoration of breeding and migratory habitat in the Central Valley.
  • In partnership with nonprofit River Partners and with funding from the Wildlife Conservation Board’s Monarch Butterfly and Pollinator Rescue Program, CDFW is restoring and enhancing 500 acres of land for monarchs and pollinators in the Central Valley.
  • On its properties throughout the state, CDFW is enhancing and restoring 1,500 acres of habitat for pollinators and monarchs through management actions and planting milkweed and nectar plants.
  • CDFW is improving management strategies on four department-owned overwintering sites.
  • CDFW is increasing milkweed availability for habitat restoration projects by collecting seed from our properties and partnering with local nurseries.
  • CDFW is also helping coordinate conservation action among stakeholders by participating in the Rangeland Monarch Working Group and co-leading the Monarch Plant Materials Working group with the Xerces Society for Invertebrate Conservation.

Julea Shaw, an environmental scientist in CDFW’s Lands Program, helps coordinate the department’s conservation and restoration efforts. Through her work, she is often reminded how California residents have a personal connection to the western monarch species.

“I speak to so many people who remember growing up seeing thousands of monarchs. It shows how impactful the species can be and how they capture peoples’ imaginations,” said Shaw.

There are several actions that residents can take to help conserve western monarchs.

First and foremost, residents can help by planting locally native milkweed and nectar plants. When choosing nectar plants, conservationists recommend choosing plants that bloom in early spring and late fall when resources tend to be scarce.

Second, residents can help by reducing or eliminating pesticide use in their own gardens.

Third, monarch enthusiasts can help conservation efforts by participating in community science projects. There are multiple organizations which train volunteers to count western monarchs at overwintering sites. In fact, much of the current data on declines in western monarch populations was collected in part by community scientists.

Finally, a note on captive rearing. CDFW would like to remind California residents that a scientific collection permit is required to handle and/or conduct research on western monarchs. Rearing monarchs without proper training can lead to health problems that further exacerbate the species’ decline. Recent research shows that captively reared monarchs can be weaker, have smaller wingspans, and be less adapted to migrate.

“It’s going to take a collective effort between residents and conservation scientists to turn the species around. We’re diligently working to expand our efforts—but the work won’t be done anytime soon,” said Sardiñas.

CDFW Photo

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